The high volume production of large area semiconductor devices, such as photovoltaic devices, is often carried out in a continuous deposition process. In processes of this type, one or more webs of substrate material are continuously advanced from a payoff station through a series of deposition chambers wherein various layers of semiconductor material are deposited thereonto, and the substrates are then wound into rolls in a take-up chamber. The deposition process often includes high vacuum conditions. Periodically, it is necessary to halt the deposition process so as to remove the coated web or webs of substrate material from the take-up station and replace them with fresh web material in the payout station, while isolation of certain process areas is maintained. In the prior art, it is standard practice to vent the entire deposition system to atmospheric pressure when changing webs of substrate material. In most instances, deposition of the semiconductor materials takes place at elevated temperatures and it is also necessary to cool the entire apparatus to ambient temperatures prior to venting it and replacing the substrate web.
The steps of cooling, venting and subsequently pumping the system back down to low pressure conditions and reheating the deposition chambers is very time consuming. In addition, exposure to ambient atmospheric conditions can introduce moisture or other contaminants into the deposition system. Therefore, the prior art has attempted to find systems which would allow for replacement of substrate webs without requiring venting of the deposition chambers of the apparatus. Toward that end, the prior art has implemented pinch valve systems in which the substrate payout station and take-up station are provided with a valving assembly which closes against a portion of a halted substrate web retained therein. In this manner, the deposition chambers of the apparatus may be maintained under vacuum conditions with a portion of the length of the substrate therein. A new web of substrate material is joined to the halted substrate web by welding it or otherwise affixing it to a portion of the substrate web projecting from apparatus of the system. Following pump down of the substrate station, the pinch valve is opened and the deposition process resumed. Pinch valves used in a system of this type must be capable of maintaining a very good seal at a pressure differential of 1 atmosphere. Also, given the fact that mechanical tolerances and spatial clearances within continuous process deposition apparatus of this type are generally quite small and very precise, any such pinch valve must not significantly deform the substrate material so as to minimize jamming, misalignment or other undesirable effects when the apparatus is restarted.
The prior art has recognized the need for pinch valves of the type described and has implemented a number of embodiments. For example, U.S. Pat. No. 5,157,851 discloses a pinch valve comprised of two movable members which engage a base. U.S. Pat. No. 6,338,872 discloses a pinch valve in which a blade-like gate member pushes a substrate against a resilient, planar, support surface. A similar pinch valve incorporating a rubber plate is described in general terms in U.S. Pat. No. 5,824,566.
As will be explained in detail hereinbelow, the present invention provides a pinch valve which is simple in construction, reliable, and which is capable of engaging a substrate so as to provide a very high isolation seal without significantly deforming or damaging the substrate. These and other advantages of the invention will be apparent from the drawings, discussion and description which follow.